Device for contactless measurement of a displacement path, especially for the detection of position and movement

ABSTRACT

The invention relates to a device ( 10 ) for contactless measurement of a displacement path, especially for the detection of position and movement, comprising a sensor electronics system for the provision of an alternating current and the evaluation of alterations therein, in addition to an inductive sensor ( 13 ) comprising at least one flat coil ( 15 ), whereby each coil ( 15 ) is configured with a helicoidal conductor ( 22 ) disposed on a plane and one of the two flat surfaces ( 19 ) thereof forms a measuring surface ( 14 ) which variously covers a measuring object ( 11 ), arranged at a distance, according to the movement thereof parallel to the measuring surface ( 14 ).

[0001] The present invention relates to a device for contactlessmeasurement of a displacement path, especially for the detection ofposition and movement, comprising a sensor electronics system for theprovision of an alternating current and the evaluation of alterationstherein, in addition to an inductive sensor comprising at least onecoil.

[0002] Similar devices, but in contrast to the displacement pathmeasurement according to the application, are known for distancemeasurement, in many different forms.

[0003] For example, from DE 196 42 699 A1, which relates to a method anda device for contactless distance measurement, in which a cylinder coilis arranged in a measuring head and the face of the measuring head islocated at a slight distance from the object to be measured, e.g. aturbine shaft, for the measurement.

[0004] In such eddy current sensors, attenuation of the magnetic fieldexiting from the sensor takes place as a function of the distance fromthe object to be measured, hereinafter also referred to as measuringobject or measuring body with attenuation trail, measuring collar,target, or the like. In other words, the attenuation is proportional tothe distance of the measuring object from the coil, so that a movementin the direction of the coil axis or longitudinal axis can be detected.For example, in order to detect the radial vibrations of a turbineshaft, an inductive sensor with a correspondingly aligned longitudinalaxis can be assigned radially to the shaft. On the basis of physicaldependencies, significant size requirements result for the measuringobject itself, in connection with predetermined coil diameters andreasonable measurement ranges; in the state of the art, this is thedistance between the coil face and the measuring object. It is true thatan axial change in the turbine shaft can also be detected with this, inthat a corresponding sensor is assigned to the shaft face with itslongitudinal axis in the axial direction. However, here again the abovedependence applies, so that significant dimensions of the objects becomenecessary for a required measurement range; in the state of the art,this is the distance. Nevertheless, eddy current sensors areadvantageous because of their robustness and their high possibleoperating temperatures, and their high limit frequencies, and are wellsuited for use.

[0005] In the state of the art, it is also generally known to detect anaxial expanse in that the known distance sensors are arranged at apreviously known angle to the measuring object. However, theaforementioned problems exist here, as well.

[0006] This means that contactless displacement path sensors accordingto the eddy current principle are well suited for distance measurements,while position measurements using these sensors, for example, requireperhaps a slanted plane on the measuring object, in order to be able todetect a displacement path portion with the distance signal, at the sametime.

[0007] In the dissertation “Untersuchung eines induktiven Spiralsensorsals Wegaufnehmer und Anwendung des Sensorelements inMikroelektronik-Systemen” [Study of an inductive spiral sensor as adisplacement path transducer and use of the sensor element inmicroelectronics systems], Fortschritt-Berichte [progress reports] VDI[Federation of German Engineers] Series 8, No. 120, VDI-Verlag,Düsseldorf, 1986, by Dieter Kohn, flat coils that were produced usingcircuit board technology are investigated. The goal was to combine asimple sensor, close to the principle, with microcomputer electronics,whereby the linearization, temperature compensation, and calibration areto be performed in the microcomputer. The flat coils are also used fordistance measurement. However, here too, an attempt is being made todirect the entire field of the coil towards the measuring object in themeasurement direction. The eddy current formation in the measuringobject that is brought about by the coil field results in an increase inthe loss resistance of the measuring coil, by way of the feedback to themeasuring coil. This change in the loss resistance is generally assessedas an attenuation change in an oscillation circuit, in the known method.The change in inductivity that also occurs is left out of considerationin this connection; in the case of non-magnetic measuring objects areduction in inductivity occurs, while in the case of magnetic measuringobjects, an increase in inductivity occurs. Here, therefore, only adistance measurement actually takes place. Furthermore, flat coils arehardly used for eddy current sensors in the state of the art, sincebundling of the magnetic field is very much poorer than inconventionally wound wire coils, because of the conductor interstices.

[0008] This, however, is extremely important in the case of the usualdistance measurement using eddy current sensors. This is because eddycurrents are produced in the measuring object proceeding from the sensorcoil, by way of the spreading magnetic field, and for this reason thefield should be as large as possible. The measuring object must beconductive and can also be magnetic. The field generated by the eddycurrents builds up a field that is opposite to the exciter field. Theeffect is all the greater, in this connection, the closer the measuringobject is located to the sensor coil. The theoretical equationrelationship, which is difficult to determine, can be found, forexample, in “Systemtechnik induktiver Weg- und Kraftaufnehmer, Aufnehmerund Anschlussgeräte” [System technology of inductive path and forcetransducers, transducers, and connection equipment], expert Verlag,Ehningen bei Böblingen, 1992, by Horst Rudolf Loos, page 52 ff.Accordingly, the eddy currents that are generated act counter to theexciting field, and reduce the self-inductivity of the exciter coil. Inthis connection, the loss resistance of the short-circuit windingdepends on the conductivity of the object material and on the distancebetween the exciter coil and the object. If, in addition, the measuringobject is magnetic, this feedback to the exciter coil is taken intoconsideration by means of the effective permeability.

[0009] The sensor coil is generally a component of an oscillationcircuit with a rather high resonance frequency of 1 to 2 megahertz. Theeddy currents of the measuring object cause an attenuation of theoscillation circuit, as a function of the distance from the measuringobject, which is then assessed. All of the inductive sensors knownaccording to the state of the art function according to the aboveprinciple, in other words that of influence on/attenuation of themagnetic field that exits from the coil, as a function of its axialdistance from the measuring object.

[0010] A principle of a differential transformer for a displacement pathmeasurement is known from a contribution by Otto Danz,“Relativdehnungsaufnehmer zur Turbinenüberwachung” [Relative expansiontransducer for turbine monitoring], in the journal Energie und Technik[Energy and Technology], October 1969, page 406 to 408. Accordingly, themeasuring collar of the turbine shaft forms a low-ohm magnetic resistor,so that the voltage at the measuring coil depends on the position of themeasuring collar. An output signal is measured at the terminals of thesecondary coil only if the symmetry has been disrupted. This happens ifthe measuring collar moves out of the center position. When aphase-controlled rectifier is used, the direction of displacement isalso recognized. This complicated principle is suitable for workingtemperatures up to approximately 350° C. and paths to be measured up toapproximately 40 mm.

[0011] Furthermore, contactless long path transducers are known from“Robuste Wegsensoren für extreme Belastungen. SENSOR '83Transducer-Technik: Entwicklung und Anwendung” [Robust displacement pathsensors for extreme stresses. SENSOR '83 transducer technology:development and application], Basel conference, May 17-19, 1983, by D.Krause, and from “Linearer, kontaktloser Umformer für grosse Wege sowiehohe thermische und dynamische Belastung” [Linear, contactlesstransformer for large displacement paths as well as great thermal anddynamic stress], Messen +Prüfen/Automatik [Measurement andtesting/automation], January/February 1981, page 43/45, by D. Krause. Inthe case of such sensors, a short-circuit ring is used as the measuringobject, which is moved in contactless manner by way of a shank of thesensor. However, in the case of these displacement path transducers, itis particularly disadvantageous that a physically caused non-linearityoccurs.

[0012] A device for measuring linear displacements of a pipe, using arod-shaped sensor coaxially arranged in the pipe, is known from DE 19832 854 A1, which makes it difficult to even provide coupling to themeasuring object.

[0013] The devices and inductive sensors known in the state of the artare therefore only poorly suited to satisfactorily accomplish the taskon which the present invention is based.

[0014] It is the task of the present invention to create a device forcontactless displacement path measurement, particularly for determiningposition and movement, which is structured in extremely simple manner,with integrating technology, and determines the movement or the positionof a measuring object, essentially independent of the contactlessdistance from it, orthogonal to the coil axis.

[0015] This task is accomplished, according to the invention, in thateach coil is configured with a helicoidal conductor disposed on a plane,and one of the two flat surfaces thereof forms a measuring surface whichvariously covers a measuring object, arranged at a distance, accordingto the movement thereof parallel to the measuring surface.

[0016] Surprisingly, it has been shown that good measurement resultsconcerning displacement path measurement are achieved if a target or ameasuring body is guided over the surface of a flat coil at a constantdistance, in contrast to the conventional sensors (for distancemeasurement), whereby only the regions covered by the target areattenuated. A linear behavior can be assured in simple manner, by way ofthe geometry of the measuring surface of the flat coils.

[0017] It is furthermore provided, according to the invention, that themeasuring surface has a triangular or square or rectangular or circularor elliptical base surface with a helicoidal arrangement of theconductors. In this way, it is easily possible to form a measuringsurface, depending on the purpose of use, that guarantees linearbehavior.

[0018] According to the invention, it is furthermore provided that thesensor has a carrier and/or a ferrite plate, and that the ferrite platecarries the flat coil directly, or holds a support plate that holds theflat coil. Accordingly, the flat coil can be arranged directly on aferrite plate, which serves to improve the coil field and the shieldingof interference effects on the back. Furthermore, a support plate can bearranged between the ferrite plate and the flat coil. The support plateparticularly serves for use in the high-temperature range. Furthermore,it can be provided that the ferrite plate is arranged on a carrier. Thecarrier generally serves for robust mounting of the ferrite plate.

[0019] It is furthermore advantageous to provide that the carrier ismade of metal or ceramic or plastic or a circuit board material, thatthe ferrite plate is made of a ferromagnetic material or a ceramic withappropriate magnetic, electrical properties, and that the support plateis made of glass or ceramic. As already mentioned, the carrier servesfor robust mounting and can be made of practically any desired material.It can therefore be integrated well into existing structures, forexample. The ferrite plate is made of the above material in order toguarantee electromagnetic shielding, in particular. Therefore thecarrier can also be made of metal, since otherwise the metallic carrierwould have the effects of a measuring object on the flat coil. Insteadof the ferrite plate, certain ceramics can also be used, which haveappropriate magnetic, electrical properties. The support platedemonstrates good suitability for high temperatures, for example up toapproximately 380° C., by means of the materials used.

[0020] It is furthermore advantageous to provide that the flat coil issputtered onto or printed onto the ferrite plate or the support plate,and that the support plate rests completely on the ferrite plate in theregion of the flat coil. In this way, particularly simple and accurateproduction methods that lie in the low-cost sector are possible, wherebymulti-plane technology, in particular, can even result in simple butaccurate reinforcement of the magnetic field.

[0021] According to the invention, it is furthermore provided that thesensor electronics system is an integral part of the inductive sensor.On the basis of the possible use of sputtering and printing technology,in particular, as well as of normal conductor tracks, integration of thesensor electronics system is particularly simple.

[0022] It is furthermore advantageous to provide that the controlelectronics are an integral part of the inductive sensor and the flatcoil. This actually makes it possible to arrange the sensor electronicssystem directly in the region of the flat coils, thereby saving space.

[0023] Furthermore, it is advantageous to provide that the flat coil ispart of an electrical oscillation circuit and has a bridge circuitintegrated into the sensor electronics system, for its attenuation orevaluation, at frequencies from kilohertz to megahertz. In this way,practically all of the advantages connected with thin-layer technologycan be utilized. This makes the sensor electronics system easy toproduce, and they can be equipped with simple components, which aresuitable for the frequencies stated, on the basis of a bridge circuit.

[0024] It is furthermore advantageous to provide that the flat coil isprinted or sputtered directly onto a silicon chip, in whole or in part,which chip also carries all the other circuits. In this way, standardcomponents with the highest quality and precision can be used directly,in accordance with the application.

[0025] Furthermore, it is advantageous to provide that the measuringobject that influences the measuring surface is electrically conductive,or that the measuring object has an electrically conductive target ormeasuring collar, and covers a coil area of the flat coil that can bepredetermined geometrically, as a function of the position of the targetor measuring collar. In this way, an electrically conductive measuringobject, which can, in addition, be magnetic, can influence the measuringsurface directly. In the case of a longitudinal expanse of a turbineaxis, actually increasingly cover. It is also possible, in the case of ameasuring object that is not electrically conductive, to arrange atarget on it and to allow it to act/utilize it accordingly. However, itis also possible to use a narrow target, similar to a strip, which movesover the measuring surface and covers a varying amount of the coilsurface, on the basis of the geometry of the measuring surface. Thedifferent attenuation is then a measure of the movement.

[0026] According to the application, it is furthermore provided that arectangular measuring surface, diagonally divided, has a triangular flatcoil, in each instance, whereby their inductive resistors and resistorsform half of a bridge circuit, the other half of which is complementedwith resistors, to produce a full bridge. This arrangement isparticularly advantageous, since it simultaneously serves forcompensation of the distance influence. This is because in case of anundesired radial movement of the measuring object, an opposite change inthe inductive resistors and resistors of the two coils takes placewhich, complemented with resistors to form a full bridge, allow ameasurement independent of distance.

[0027] According to a particular embodiment, it is furthermore providedthat a second sensor, with a measuring surface diagonally divided intotwo flat coils, is arranged in such a way that the measuring object liessymmetrically between the two sensors and that the two flat coils ofeach sensor, in each instance, form the inductive resistors andresistors of half of the bridge circuit, in each instance. In this way,signal doubling can take place, with simultaneous compensation of theundesired radial distance influence. In connection with a phase-correctrectifier, a movement of the measuring object, with the correct sign,can be indicated, starting from the zero position.

[0028] It is furthermore advantageous to provide that a rectangularmeasuring surface, diagonally divided, has two triangular flat coils,whereby the inductive resistor and the resistor of one flat coil and acomplementary resistor form one half of a bridge circuit, whose otherhalf is diagonally complemented with inductive resistor and resistor andanother complementary resistor to form a full bridge. Particularly inthe case of increasing full coverage of a correspondingly divided flatcoil, this diagonal bridge has demonstrated a qualitatively high andessentially distortion-free evaluation, which takes the increasingcoverage for both flat coils appropriately into consideration.

[0029] According to the application, it is furthermore provided that thetarget or the measuring collar is adapted to the measuring object and/orrectangular and/or bow-shaped and/or ring-shaped. Particularly in thecase of measurements of piston positions of compressed air or pneumaticcylinders, as well as a cone of flow-through measuring devices, simpleadaptation to the measurement purpose can take place in this way.

[0030] Furthermore, it is provided, according to the invention, that themeasuring surface of the sensor for a movement measurement of balls orrollers in bearings is arranged in their central vicinity and has asmaller cross-sectional surface than the measuring object. In this way,the device is actually suited to reliably guarantee the movements ofmicroparts, without any other technical effort.

[0031] Furthermore, it is advantageous to provide that the measuringsurface of the sensor is shaped like an arc, in order to determinemovement on an arc. In this way, even angle measurements are possible,i.e. a displacement path measurement along an arc.

[0032] Furthermore, it is advantageous to provide that the measuringsurface of a sensor has a great change in surface in a region with thedesired greatest resolution. In this way, it is possible to achievecharacteristic signal images when moving past certain shaped parts, forexample, such as coins, so that the device according to the invention isalso suitable for sorting coins, for example.

[0033] Furthermore, it is provided, according to the invention, that arectifier is an integral part of the sensor electronics system. Asalready mentioned, it is easily possible, in connection with aphase-correct rectifier, to indicate a movement of the measuring objectfrom the zero position, with the correct sign.

[0034] It is advantageous to provide that Schmitt trigger electronicsare an integral part of the sensor electronics system, and that thesensor electronics system emits a threshold signal. In this way,threshold value switches can be built.

[0035] It is furthermore advantageous to provide that the device iscompletely arranged within a housing. In this way, it is compact andprotected from environmental influences, and can be reliably used evenunder robust ambient conditions.

[0036] In summary, the invention is therefore based on a measuring coilas a flat coil, which is constantly crossed in contactless manner, at aconstant, slight distance from a measuring object. For example, for thepurpose of linear behavior, the measuring surface can be configured tobe triangular. With a measuring collar on a turbine shaft, the radialexpanse of the turbine shaft can therefore be determined with this. Inthis connection, advantage is taken of the fact that the magnetic fieldformed around itself by each conductor is influenced by the localcoverage of the measuring object only in accordance with the coveragearea, by way of the eddy current effect. When the measuring object ismoved from one position to another, an increasing or decreasing coverageof conductor parts of the measuring oil takes place, as a function ofthe measuring path. In this connection, the measuring object can crossthe measuring coil as a strip or, alternatively, can cover itincreasingly completely, for example as a rectangular measuring object.The transformation of the measuring path into an electrical measuringsignal can take place, in the case of the known methods, by way of anoscillation circuit, the inductive resistor of which consists of themeasuring coil, and which is supplied by an oscillator. It has proven tobe particularly advantageous for the invention to use an alternatingcurrent bridge circuit. The triangular flat coil, for example,represents an inductive resistor and a resistor, and an opposite furthertriangular flat coil, which complements the first to form a rectangle,represents another inductive resistor and another resistor. If themeasuring object is moved from one position to another, an oppositechange in the inductive resistors and resistors of the flat coils takesplace. These inductive resistors and resistors form one half of a bridgecircuit, and can be complemented with resistors on the other half, toform a full bridge. In this way, a measuring voltage that isproportional to the displacement of the measuring object can be tappedbetween the measuring points of a bridge circuit. In connection with aphase-correct rectifier, a movement of the measuring object out of thezero position, with the correct sign, can therefore be indicated. Theadvantages of the bridge circuit lie, in particular, in the reduction inthe temperature dependence of the measuring effects and in thedependence on distance. For this purpose, an additional symmetricalmeasuring arrangement can be provided in order to double the measuringsignal. A diagonal bridge circuit has the advantages described above.

[0037] Other preferred embodiments of the invention are evident from thedependent claims.

[0038] An exemplary embodiment of the invention will be explained ingreater detail below, on the basis of a drawing. This shows:

[0039]FIG. 1 schematically, a device according to the invention, withregard to a measuring object, with one sensor,

[0040]FIG. 2 schematically, a device according to the invention inaccordance with FIG. 1, with two sensors,

[0041]FIG. 3 schematically, the measuring surface of a sensor of adevice according to the invention, and

[0042]FIG. 4 an equivalent circuit schematic of a bridge circuit fordetermining the measuring result in the case of multi-coil sensors.

[0043]FIG. 1 shows a device 10 according to the invention, forcontactless displacement path measurement, for example of a shaft 11,which can be a turbine shaft and moves in its longitudinal expanse, fromleft to right in FIG. 1, as indicated with broken lines 12 and arrow D.The device 10 has an inductive sensor 13 that is arranged at a distancefrom the shaft 11. The sensor 13 has a flat measuring surface 14, whichis formed by a flat coil 15.

[0044] The flat coil 15 can be arranged directly on a ferrite plate 16,or first on a support plate 17, which in turn is arranged on the ferriteplate 16. The ferrite plate 16 itself is, in turn, arranged on a carrier18, which gives it support and can be made of practically any desiredmaterial, for example metal, plastic, circuit board material or also aceramic. The ferrite plate 16 is made of ferromagnetic material, or alsoa ceramic with appropriate electrical, magnetic properties. It serves toshield electromagnetic effects on the part of the carrier 18, which cantherefore also be made of metal. In other words, the second surface 19of the flat coil 15, which faces away from the measuring surface 14, isrigidly arranged on a substratum and free of any electromagneticinfluences. The support plate 17 generally serves as a thermally robustsupport of the flat coil 15. By using glass or ceramic for the supportplate 17, temperatures of up to 380° C. can be safely achieved.

[0045] A particularly simple device 10 can actually consist only of theferrite plate 16 and the flat coil 15, arranged directly on it, if thematerials are selected in a special way. The support plate 17 and thecarrier 18 are eliminated.

[0046] The device 10 furthermore comprises a sensor electronics systemwhich, however, is not shown in detail, with oscillation circuits, etc.,a bridge circuit 20, and a rectifier circuit, with the necessaryelements and connections.

[0047] The shaft 11 moves in the direction of the arrow D. It carries ameasuring collar/target 21, which must be electrically conductive andcan also be magnetic. In the case of movement in the direction of arrowD, the shaft 11, and therefore also the target 21 moves parallel andorthogonal to the measuring surface 14. The measuring surface 14 of theflat coil 15 has at least one conductor 22 per flat coil 15, which isarranged in helicoidal form in the plane of the measuring surface 14.Advantageously, the conductor 22 can be arranged helicoidally in such away that the base surface of the measuring surface 14 is triangular.Even without studying FIG. 3, it can be imagined that in the case of atriangular measuring surface 14, if the target 21 moves, more or fewerconductors 22 are covered by the target 21. Therefore, more or fewereddy currents are produced in the target 21 which, in the finalanalysis, have an attenuation effect on the inductive sensor 21 andallow the evaluation of a position signal. In the case of a specificmaterial selection, the shaft 21 itself can also allow a correspondingsignal by means of a greater or lesser coverage of the measuring surface14.

[0048] In the case of other movements to be detected, the conductor 22can have a geometrically different shape; for example, a square orrectangular or circular or elliptical measuring surface 14 can beformed. However, it has proven to be advantageous that in the case ofthe radial expanse measurement of a shaft 11, as shown, radial movementsresulting from vibrations, etc., of the shaft 11 itself result inmeasuring variations, since the electromagnetic field to the flat coil15 is greatly dependent on distance. This influence can be eliminated,according to the application, in extremely simple manner, in thatanother triangular measuring surface 14 is arranged in such a way,together with a first flat coil 15, that a diagonally dividedrectangular or square total/measuring surface 14 is formed. If evaluatedappropriately, the changes in the opposite coil signals can result in anelimination of the distance effect.

[0049]FIG. 2 shows two devices 10, the measuring surfaces 14 of whichare arranged parallel and at a distance from one another and oppositeone another. The distance between the measuring surfaces 14 isdimensioned in such a way that the shaft 11 can be arrangedsymmetrically between the two devices 10. While keeping theconfiguration of the individual devices 10 and also of the shaft 11 withthe target 21 otherwise the same, signal doubling can be achieved inthis way, in extremely simple manner. Of course it is also possible toarrange other devices 10 accordingly, in the circumference region of theshaft 11, and to pass the data individually obtained from the devices 10on to assessment externally. In this way, not only can a reinforcementof the output signal be achieved, but also the measuring accuracy can beincreased, as well as the detection of complex surface displacements onan object, which occur, for example, in the case of tensile tests of anydesired objects.

[0050]FIG. 3 shows the device 10 in a top view onto the measuringsurface 14. Two flat coils 15 with one conductor 22 each, with atriangular base surface, in each instance, can easily be seen, wherebythe flat coils 15 complement one another to form a rectangulartotal/measuring surface 14. Here again, the target 21 is indicated,which is moved in the direction of arrow D up to the position 21 shownwith a broken line, and in this connection covers, i.e. physicallycovers differently many coil segments, in the final analysis, surfacesof the flat coil 15. In accordance with the geometry, this takes placein opposite directions, i.e. it takes place increasingly for the onecoil, and decreasingly to the same extent for the other coil 15. In thisconnection, the flat measuring surface 14 is arranged centrally on thesupport plate 17, which in turn is attached to the larger ferrite plate16. The ferrite plate 16 always has a greater expanse than the measuringsurface 14 and therefore also than the support plate 17, in order toassure complete shielding of the measuring surface 14, in other words ofthe inductive sensor 12, on the side of the surface 19 towards thecarrier 18.

[0051] Although it is not shown, the control electronics system with allof its elements, including the oscillation circuit, the bridge circuit20, if necessary a Schmitt trigger, etc., can be structured with thesame technology as the flat coil 15 itself, and can be arranged directlyon the measuring surface 14. Sputtering technology has proven to beparticularly advantageous for this, or also the technology of printedcircuits, also directly onto a silicon chip, which then can also containthe electrical circuits. Both are techniques that can be carried outwith a single layer or multiple layers, and are available at a lowprice, at high quality.

[0052]FIG. 4 shows a bridge circuit 20. The bridge circuit 20 consistsof a first half 23 according to line A-A, with alternatives in thebottom bridge branch according to line a-a and b-b, and a second half 24according to line B-B or C-C or D-D. This is preferably a Wheatstonebridge circuit for alternating current. In the case of only one device,according to FIG. 1, with a total/measuring surface 14 with two flatcoils 15 according to FIG. 3 and a narrow target 21, a bridge circuit 20in which the inductive resistor 25 and the resistor 26 of the first flatcoil 15 and the inductive resistor 27 and the resistor 28 of the secondflat coil 15 are in contact in the first half 23 according to the lineA-A and a-a has proven to be advantageous. The plugs 42 that areindicated are brought into contact. By moving the target 21 according toFIG. 3, an opposite change in the corresponding inductive resistors 25and 27 and the resistors 26 and 28, on the other hand, takes place. Inthis case, the resistors 29 and 30 form the bridge complement to formthe full bridge in the second half 24 according to the line B-B of thebridge circuit 20. Between the measuring points 31, 32, the measuringvoltage, which is proportional to the displacement of the measuringobject, can be tapped. In this case, the plugs 33 that are indicated arebrought into contact.

[0053] In the case of two sensors 13 according to FIG. 2, with two flatcoils 15 each per total/measuring surface 14, it is possible, accordingto an advantageous and extremely simple bridge circuit 20, to contactthe second half 24 according to C-C, instead of the second half 24according to B-B, by way of the plugs 34, which complements the firsthalf 23 of the bridge circuit 20 according to line A-A and a-a, to forma full bridge, while leaving the circuitry of the first half 23 thesame. The inductive resistor 35 and the resistor 36 represent thecharacteristic values of the first flat coil 15 of the second sensor 13,and the inductive resistor 37 and the resistor 38 represent thecharacteristic values of the second flat coil 15 of the second sensor13. Here again, a measuring voltage that is proportional to thedisplacement of the measuring object can be tapped between the measuringpoints 31 and 32. In connection with a phase-correct rectifier, notshown, a movement of the measuring object 11 from the zero position,with the correct sign, can be indicated.

[0054] In the case of a sensor 13 according to FIG. 2, with two flatcoils 15 according to FIG. 3, and a target 21 that increasingly ordecreasingly covers the total/measuring surface 14, a bridge diagonalcircuit 20 has proven to be extremely advantageous, in which theinductive resistor 25 and the resistor 26 of the first flat coil 15 ofthe first half 23 are arranged in the top bridge branch, according tothe line A-A, while the inductive resistor 27 and the resistor 28 of thesecond coil 15 of the second half 24 are arranged in the bottom bridgebranch, according to the line D-D, whereby the second half 24 comes intocontact by way of the plugs 44. The resistors 39 and 40 that complementthe bridge circuit are connected, i.e. arranged according to the lineA-A and b-b in the first half 23, by way of the plugs 43, and in the topbridge branch in the second half 24. With this diagonal bridge circuit20, a measuring voltage that is proportional to the displacement of themeasuring object can be tapped between the measuring points 31 and 32.

[0055] The advantages of the proposed bridge circuit 20 lie, inparticular, in the reduction of the temperature dependence of themeasuring effects and of the distance dependence.

[0056] The characteristics of the invention as disclosed in the abovespecification, in FIGS. 1 to 4, as well as in the claims, can beessential for implementing the invention in its various embodiments,both individually and in any desired combination.

1. Device for contactless measurement of a displacement path, especiallyfor the detection of position and movement, comprising a sensorelectronics system for the provision of an alternating current and theevaluation of alterations therein, in addition to an inductive sensorcomprising at least one coil, characterized in that each coil (15) isconfigured with a helicoidal conductor (22) disposed on a plane, and oneof the two flat surfaces thereof forms a measuring surface (14) whichvariously covers a measuring object (11), arranged at a distance,according to the movement thereof parallel to the measuring surface(14).
 2. Device according to claim 1, characterized in that themeasuring surface (14) has a triangular or square or rectangular orcircular or elliptical base surface with a helicoidal arrangement of theconductors (22).
 3. Device according to claim 2, characterized in thatthe sensor (13) has a carrier (18) and/or a ferrite plate (16), and thtthe ferrite place (16) carries the flat coil (15) directly, or holds asupport plate (17) that holds the flat coil (15).
 4. Device according toclaim 3, characterized in that the carrier (18) is made of metal orceramic or plastic or a circuit board material, that the ferrite plate(16) is made of a ferromagnetic material or a ceramic with appropriatemagnetic, electrical properties, and that the support plate (17) is madeof glass or ceramic.
 5. Device according to claim 4, characterized inthat the flat coil (15) is sputtered onto or printed onto the ferriteplate (16) or the support plate (17), and that the support plate (17)rests completely on the ferrite plate (16) in the region of the flatcoil (15).
 6. Device according to claim 5, characterized in that thesensor electronics system is an integral part of the inductive sensor(13).
 7. Device according to claim 6, characterized in that the controlelectronics are an integral part of the inductive sensor (13) and theflat coil (15).
 8. Device according to claim 6 or 7, characterized inthat the flat coil (15) is part of an electrical oscillation circuit andhas a bridge circuit (20) integrated into the sensor electronics system,for its attenuation or evaluation, at frequencies from kilohertz tomegahertz.
 9. Device according to one or more of the preceding claims,characterized in that the flat coil (15) is printed or sputtereddirectly onto a silicon chip, in whole or in part, which chip alsocarries all the other circuits.
 10. Device according to one or more ofthe preceding claims, characterized in that the measuring object (11)that influences the measuring surface (14) is electrically conductive,or that the measuring object (11) has an electrically conductive target(21) or measuring collar (21), and covers a coil area of the flat coil(15) that can be predetermined geometrically, as a function of theposition of the target (21) or measuring collar (21).
 11. Deviceaccording to claim 10, characterized in that a rectangular measuringsurface (14), diagonally divided, has a triangular flat coil (15), ineach instance, whereby their inductive resistors (25, 27) and resistors(26, 28) form half (23) of a bridge circuit (20), the other half (24) ofwhich is complemented with resistors (29, 30), to produce a full bridge.12. Device according to claim 11, characterized in that a second sensor(13), with a measuring surface (14) diagonally divided into two flatcoils (15), is arranged in such a way that the measuring object (11)lies symmetrically between the two sensors (13) and that the two flatcoils (15) of each sensor (13), in each instance, form the inductiveresistors (25, 27 and 35, 37) and resistors (26, 28 and 36, 38) of half(23, 24) of the bridge circuit, in each instance.
 13. Device accordingto one or more of the preceding claims, characterized in that arectangular measuring surface (14), diagonally divided, has twotriangular flat coils (15), whereby the inductive resistor (25) and theresistor (26) of one flat coil (15) and a complementary resistor (39)form one half (23) of a bridge circuit (20), whose other half (24) isdiagonally complemented with inductive resistor (27) and resistor (28)and another complementary resistor (40) to form a full bridge. 14.Device according to one or more of the preceding claims, characterizedin that the target (21) or the measuring collar (21) is adapted to themeasuring object (11) and/or rectangular and/or bow-shaped and/orring-shaped.
 15. Device according to one or more of the precedingclaims, characterized in that the measuring surface (14) of the sensor(13) for a movement measurement of balls or rollers in bearings isarranged in their central vicinity and has a smaller cross-sectionalsurface than the measuring object (11).
 16. Device according to one ormore of the preceding claims, characterized in that the measuringsurface (14) of the sensor (13) is shaped like an arc, in order todetermine movement on an arc.
 17. Device according to one or more of thepreceding claims, characterized in that the measuring surface (14) ofthe sensor (13) has a great change in surface in a region with thedesired greatest resolution.
 18. Device according to one or more of thepreceding claims, characterized in that a rectifier is an integral partof the sensor electronics system.
 19. Device according to one or more ofthe preceding claims, characterized in that Schmitt trigger electronicsare an integral part of the sensor electronics system, and that thesensor electronics system emits a threshold signal.
 20. Device accordingto one or more of the preceding claims, characterized in that the deviceis completely arranged within a housing.